ABSTRACT We present the results of precision gamma-ray timing measurements of the binary millisecond pulsar PSR J2339-0533, an irradiating system of the "redback" type, using data from the Fermi ...Large Area Telescope. We describe an optimized analysis method to determine a long-term phase-coherent timing solution spanning more than six years, including a measured eccentricity of the binary orbit and constraints on the proper motion of the system. A major result of this timing analysis is the discovery of an extreme variation of the nominal 4.6 hr orbital period over time, showing alternating epochs of decrease and increase. We inferred a cyclic modulation of with an approximate cycle duration of 4.2 yr and a modulation amplitude of . Considering different possible physical causes, the observed orbital-period modulation most likely results from a variable gravitational quadrupole moment of the companion star due to cyclic magnetic activity in its convective zone.
Fully coherent searches (over realistic ranges of parameter space and year-long observation times) for unknown sources of continuous gravitational waves are computationally prohibitive. Less ...expensive hierarchical searches divide the data into shorter segments which are analyzed coherently, then detection statistics from different segments are combined incoherently. The novel method presented here solves the long-standing problem of how best to do the incoherent combination. The optimal solution exploits large-scale parameter-space correlations in the coherent detection statistic. Application to simulated data shows dramatic sensitivity improvements compared with previously available (ad hoc) methods, increasing the spatial volume probed by more than 2 orders of magnitude at lower computational cost.
We have obtained initial spectroscopic observations and additional photometry of the newly discovered P sub(b) = 94 minute gamma -ray black-widow pulsar PSR J1311-3430. The Keck spectra show a ...He-dominated, nearly H-free photosphere and a large radial-velocity amplitude of 609.5 + or - 7.5 km s super(-1). Simultaneous seven-color GROND photometry further probes the heating of this companion, and shows the presence of a flaring infrared excess. We have modeled the quiescent light curve, constraining the orbital inclination and masses. Simple heated light-curve fits give M sub(NS) = 2.7 M sub(middot in circle), but show systematic light-curve differences. Adding extra components allows a larger mass range to be fit, but all viable solutions have M sub(NS) > 2.1 M sub(middot in circle). If confirmed, such a large M sub(NS) substantially constrains the equation of state of matter at supernuclear densities.
We present the results of precision gamma-ray timing measurements of the binary millisecond pulsar PSR J2339–0533, an irradiating system of the “redback” type, using data from the Fermi Large Area ...Telescope. We describe an optimized analysis method to determine a long-term phase-coherent timing solution spanning more than six years, including a measured eccentricity of the binary orbit and constraints on the proper motion of the system. A major result of this timing analysis is the discovery of an extreme variation of the nominal 4.6 hr orbital period P{sub orb} over time, showing alternating epochs of decrease and increase. We inferred a cyclic modulation of P{sub orb} with an approximate cycle duration of 4.2 yr and a modulation amplitude of ΔP{sub orb}/P{sub orb}=2.3×10{sup −7}. Considering different possible physical causes, the observed orbital-period modulation most likely results from a variable gravitational quadrupole moment of the companion star due to cyclic magnetic activity in its convective zone.
Here, we report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search ...approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422–6138, J1522–5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range 6 × 1034—1036 erg s–1. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hz spin frequency of PSR J0554+3107 is the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources.
The Einstein@Home Survey for Gamma-ray Pulsars Clark, Colin J.; Wu, Jason; Pletsch, Holger J. ...
Proceedings of the International Astronomical Union,
09/2017, Letnik:
13, Številka:
S337
Journal Article
Recenzirano
Odprti dostop
Since the launch of the Fermi Gamma-ray Space Telescope in 2008, the onboard Large Area Telescope (LAT) has detected gamma-ray pulsations from more than 200 pulsars. A large fraction of these remain ...undetected in radio observations, and could only be found by directly searching the LAT data for pulsations. However, the sensitivity of such “blind” searches is limited by the sparse photon data and vast computational requirements. In this contribution we present the latest large-scale blind-search survey for gamma-ray pulsars, which ran on the distributed volunteer computing system, Einstein@Home, and discovered 19 new gamma-ray pulsars. We explain how recent improvements to search techniques and LAT data reconstruction have boosted the sensitivity of blind searches, and present highlights from the survey’s discoveries. These include: two glitching pulsars; the youngest known radio-quiet gamma-ray pulsar; and two isolated millisecond pulsars (MSPs), one of which is the only known radio-quiet rotationally powered MSP.
Blind Search Methods for Binary Gamma-ray Pulsars Nieder, Lars; Clark, Colin J.; Pletsch, Holger J.
Proceedings of the International Astronomical Union,
09/2017, Letnik:
13, Številka:
S337
Journal Article
Recenzirano
Odprti dostop
Gamma-ray observations by the Fermi Large Area Telescope (LAT) have been used very successfully in the last 9 years to detect more than 200 gamma-ray pulsars. Sixty of these have been found by ...directly searching for pulsations in the gamma-ray data, but only one binary MSP has been found this way. Pulsars in binaries are often difficult to detect in radio data because of large eclipses, and some binary MSPs may even be radio quiet. For those, a gamma-ray blind search might be the only possibility for detection. While searches for isolated pulsars up to kilohertz frequencies are already computationally very challenging, blind searches for binary gamma-ray pulsars are simply infeasible without further knowledge of their orbital parameters. Here we present methods with which we can conduct searches for candidate binary gamma-ray pulsars for which orbital constraints are known from optical observations of a likely companion star. We also highlight some example sources where these methods have been used.
Placing signal templates (grid points) as efficiently as possible to cover a multidimensional parameter space is crucial in computing-intensive matched-filtering searches for gravitational waves, but ...also in similar searches in other fields of astronomy. To generate efficient coverings of arbitrary parameter spaces, stochastic template banks have been advocated, where templates are placed at random while rejecting those too close to others. However, in this simple scheme, for each new random point its distance to every template in the existing bank is computed. This rapidly increasing number of distance computations can render the acceptance of new templates computationally prohibitive, particularly for wide parameter spaces or in large dimensions. This paper presents a neighboring cell algorithm that can dramatically improve the efficiency of constructing a stochastic template bank. By dividing the parameter space into subvolumes (cells), for an arbitrary point an efficient hashing technique is exploited to obtain the index of its enclosing cell along with the parameters of its neighboring templates. Hence only distances to these neighboring templates in the bank are computed, massively lowering the overall computing cost, as demonstrated in simple examples. Furthermore, we propose a novel method based on this technique to increase the fraction of covered parameter space solely by directed template shifts, without adding any templates. As is demonstrated in examples, this method can be highly effective.
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